Multimode-Responsive Luminescence of Er³⁺ Single-Activated CaF₂ Phosphor for Advanced Information Encryption

Abstract

The current optical anticounterfeit strategies that rely on multimode luminescence in response to the photon or thermal stimuli have significant importance in the field of anticounterfeiting and information encryption. However, the dependence on light and heat sources might limit their flexibility in practical applications. In this work, Er 3+ single-doped CaF 2 phosphors that show multistimuli-responsive luminescence have been successfully prepared. The as-obtained CaF 2 :Er 3+ phosphor exhibits green photoluminescence (PL) and color-tunable up-conversation (UC) luminescence from red to green due to the cross-relaxation of Er 3+ ions. Additionally, as-obtained CaF 2 :Er 3+ phosphors also display green mechano-luminescence behavior, which is induced by the contact electrification between the CaF 2 particles and PDMS polymers, enabling the phosphor to flexibly respond to mechanical stimuli. Moreover, feasible anticounterfeiting schemes with the capability of multistimuli-responsive and flexible decryption have been constructed, further expanding the application of optical materials in the field of advanced anticounterfeiting and information encryption.

Multicolor and multimodal luminescence in an Er3+ single-doped double perovskite for advanced anti-counterfeiting and encryption

“…1e and inset). 26 A representative SEM micrograph of the NGTAO:1.0%Er 3+ sample reveals a relatively regular morphology with an average size of 1–5 μm (Fig. 1f and inset).…”

“…This observation confirms the energy transfer from Er 3+ to defect levels. 26 In addition, the decay curves of red emission exhibit a long temporal tail, which correlates to the red afterglow. 31,32 The photos (Fig.…”

“…This range corresponds to the characteristic excitation of NGTAO:Er 3+ , originating from the 4 I 15/2 → 4 G 11/2 and 4 I 15/2 → 2 H 9/2 transitions of Er 3+ . 26 Importantly, the excitation regions of red and green emissions have a partial spectral overlap in the 360–395 nm range, indicating that tunable color in the red-green range of NGTAO:Er 3+ can be obtained through simultaneously pumping different ratios of green/red emission by adjusting the excitation wavelength. Microstructures such as defects also play an important role in intrinsic luminescence.…”

Theoretical Determination of the Electronic Structures and Energy-Level Splitting for Pr3+-Doped Y2SiO5 Crystals

“…Rare-earth (RE)-doped crystals play a pivotal role in the development of emitting optics and luminescent materials. − Due to the generous optical spectrum and transitions lines of 4f electrons, the RE ion-doped crystals are widely used in photoluminescence, X-ray imaging, optical communication, and medical diagnosis. − The yttrium silicate (Y 2 SiO 5 ) crystal is first synthesized by Warshaw and Roy . It is a vital laser host crystal that has attracted wide attention.…”

“…More importantly, the host Y 2 SiO 5 is a monoclinic crystal with a C 2 space group . Y atoms can be coordinated with seven oxygen atoms or six oxygen atoms, thus forming the local [YO 7 ] −11 or [YO 6 ] −9 complex ligands, respectively. This multisite ligand structure could provide suitable doping sites for many RE ions.…”